Focus by Cabana Labs

Focus breaks bad habits by taking you to a beautiful page whenever you type in your favorite distracting websites.

Focus breaks bad habits by taking you to a beautiful page whenever you type in your favorite distracting websites.
To get started, install the add-on.
A new orange button will appear in the top-right corner of your browser window.
Press on the orange button to reveal the editor.
In the editor, simply type in the websites that you'd like to block, one per line, then press Save.
That's it. Now if you try to visit that website, you'll automatically be redirected to a page with the current time and a beautiful picture on it to help you stay focused!
You can also set Office Hours through the Extension's Options from your browser's Preferences screen!
You can now set your own default website to redirect to from the Extension's Options! Make sure you set the full URL including the "http" part! =)